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MatchCard Science Conservation of Mass
Objective: Explain the law of conservation of mass.
MatchCard: Download below.
Students give examples of conservation of mass and answer true and false questions.
Projects: Sizzle and Burn. Burn a log or sheet of paper. Dissolve an seltzer tablet and weigh the results.
Download and Use the Conservation of Mass MatchCard
This is MatchCard #11 of the Chemistry Unit Study. Find more information on MatchCard Science below.
Introduce the Conservation of Mass
Unless you have a fireplace, this first example of conservation of mass is best discussed than demonstrated.
Ask what happens to wood when it burns. It looks like the wood is destroyed.
When a piece of wood is burnt in a fireplace, only a small amount of ashes are left. It appears that the fire destroyed the wood and that most of the substance in the wood is completely gone.
As an alternative, it is possible to burn a piece of paper in an outdoor grill or other appropriate container. Obviously, discuss fire safety and appropriate use of matches with kids as needed.
We are going to do a little experiment to show that matter is never completely destroyed - at least in a scientific sense.
For this experiment you will need:
- a small scientific, kitchen, or postal scale
- Disposable bathroom cup or other small, light weight container
- One quarter cup of water
- One Alka-seltzer tablet
- One small ziploc bag
To begin with, weigh the cup with the quarter cup of water in it. Write down the weight. Next weigh the Alka-Seltzer tablet. Add the two amounts to find the combined weight.
Now, drop the tablet in the water. Watch the chemical reaction.
When the sizzling is finished, weigh the cup again.
Oops, it weighs less than the combined weight before they were added. It LOOKS as if some matter disappeared.
Now, let's do it again and see what happened to that missing weight. Add one quarter cup of water into a small ziploc bag. Seal the bag and weigh it.
Now drop the tablets into the bag and seal it QUICKLY. Enjoy watching the experiment again.
When you weigh the ziploc bag after the reaction is done you will find it is the same as the weight of all the substances before the experiment. Ask the student to explain the difference. They should be able to discern that the gas that escaped in the chemical experiment was still in the bag but not in the cup.
It's a neat little example of the conservation of mass. The chemical matter was changed, but it still existed in a different form.
Learn About the Conservation of Mass
Another example is burning of coal. Use the information pieces from Chemistry Matchcard 11 (download below) to demonstrate this principle.
Coal is made up of carbon. Put the "C" for carbon on the table.
When coal is burned in a coal burning stove, it looks like it is destroyed just as it looks like wood is destroyed in a fireplace. But the chemical matter does not disappear. A substance can only burn in the presence of oxygen. Put "O2
" chemical symbol on the table near the symbol for carbon.
When coal is burned, the carbon combines with the oxygen to produce carbon dioxide. Place the CO2
symbol on the table. Carbon dioxide is a gas and we can't see it. But neither the carbon nor the oxygen were destroyed. The atoms reformed into different molecules, but the atoms still existed.
The conservation of mass tells us that the number of atoms after a chemical reaction will always be the same as the number before the reaction. Substances change, but they are not destroyed.
Teacher’s Note: Sometimes the burning of coal results in carbon moxoide where 2 carbon atoms react with 1 oxygen molecule to produce 2 carbon monoxide molecules. The chemical formula is (2)C + 02 = (2)CO. This formula is a little more complex.
What's In A Name?
“Conserve” means to keep or save. “Conservation” is the noun form of the word “conserve.” Can you explain the phrase “Conservation of Matter?”